Aluminum clad magnesium and method of making same



Nov. 10, 1942. SCHELLER I 2,301,332

ALUMINUM GLAD MAGNESIUM AND METHOD OF MAKING SAME Filed April 26, 1940ALUMINUM of? ALUMINUM ALLOY C o1 z/Nc ALLOY ALL- Ernest Sc/Lel 34343Camman, Mn f/zZZTnL Mac/ Patented Nov. 10, 1942 UMINUM GLAD MAGNESIUMAND METHOD OF MAKING SAME Ernest Scheller, Louisville, Ky., assignor toReynolds Metals Company, New York, N. Y., a

corporation of Delaware Application April 26, 1940, Serial mensesClaims. (Cl. 29-189) This invention relates to the production ofcomposite bodies of magnesium and aluminum.

A composite body composed of laminations of magnesium and aluminum ispossessed of numerous important advantages in the electrical, mechanicaland chemical arts, because of the relative and diverse characteristicspossessed by aluminum and magnesium which particularly fit them for useas coating and core metals in composite metal structures. Thus aluminumis more resistant to galvanic action than magnesium and tends topreserve itself at the expense of magnesium; magnesium has asubstantially lower specific gravity than aluminum, and therefore wherelighter weight per unit of cross-sectional area or greater stifiness andstrength per unit of the cross-sectional weight are desirable magnesiumis a highly desirable body material, but magnesium corrodes easily andchemical treatments to render it resistant to corrosion increase thecost and impair some of the desirable characteristics of magnesium;while both metals are strong and have similar melting temperatures,coeificients of expansion and," contraction, etc., aluminum has higherelectrical and thermal conductivity, greater reflectivity, is moreresistant to abrasion, chemical reaction, corrosion, etc.

The bonding of magnesium toaluminum presents grave practicaldifficulties. The high surface tension, tenacity and resistance torupture of aluminum and magnesium oxide films, existing on aluminum andmagnesium in the presence of air, render difficult the adhesion ofmagnesium to aluminum even though an effort be made to roll the twotogether under relatively high pressures and at elevated temperaturesbecause of the difiiculty of breaking through these tenacious oxidefilms. Furthermore when aluminum and magnesium are permitted to unite,by dispersion or otherwise; they form very brittle compounds, in fact sobrittle that some of them will shatter like glass, while such compoundsor mixtures are so hard as to make extremely difiicult, if notimpossible, the rolling down to thin sheets, foils and the like oflayers of aluminum and magnesium united by an aluminum-magnesium bond.

It is an object of this invention to provide an improved method wherebymagnesium may be satisfactorily used for the fabrication of a widevariety of articles where weight is' important.

Another object of this invention is, to provide an improved methodwhereby magnesium'may be suitably protected against corrosion.

Another object of, this invention is to provide nesium is facilitatedand a greater variety of lubricants may be used.

Another object of this invention is to produce laminated magnesium andalumimun by a procedure which assures a substantially unifonn bondthroughout the contiguous surfaces of the laminations withoutestablishing a hard or brittle aluminum-magnesium bond between the same.

Another object of this invention is to provide an improved method forproducing laminated bodies of aluminum and magnesium wherein the bondconnecting the laminations may be so.

coated magnesium wherein the laminations are united throughoutcontiguous surfaces thereof while preserving the desirablecharacteristics of the magnesium as a core metal and of the aluminum asa surface metal and avoiding hard or brittle layers ofaluminum-magnesium compounds.-

Another object of this invention is to provide an improved magnesiumbody which is completely and permanently coated with a corrosionpreventing envelope and which can therefore be widely used wheredecreased weight or decreased corrosion or increased strength orstiffness per unit of cross-sectional weight is desirable.-

Another object of this invention is to produce an improved aluminumcoated magnesium which can be readily drawn, rolled, pressed, shaped andotherwise worked, and therefore fabricated into a wide variety ofarticles and applied to a wide variety of uses, but with the assurancethat the bond between the laminations will not be of such a characterthat it will be destroyed by or interfere with such operations thereon,

Another object of this invention is to produce aluminum coated magnesiumwhich, while preserving the desirable characteristics of magnesium as acore metal and aluminum as a surfacing metal, also secures variousadvantages to be derived from their association in laminations withoutinterfering with or detracting from the desired characteristics of suchcomposite metal bean improved method whereby the rolling of mag- Cause fcompounds arising the i tion of these two metals into a laminated structure.

In Letters Patent No. 2,100,257 granted November 23, 1937, to Clayton E.Larson, for Composite bodies of magnesium and aluminum, and method ofmaking same, one method of uniting cores of magnesium with an envelopeor surface laminations of aluminum has been described, this methodincluding the casting of a magnesium core into an aluminum envelope orbetween aluminium plates provided with zinc bonding layers. Owing to thesmall difference between the melting temperatures of aluminum andmagnesium it is difficult to cast magnesium into such an aluminumenvelope without effecting a substantial dispersion of the magnesiuminto the aluminum, notwithstanding the presence of the zinc layer, withthe consequent development of hard aluminummagnesium compounds.Furthermore experience has demonstrated that cast magnesium which hasnot been subjected to grain refinement is difficult to roll or otherwisework.

It is an object of the present invention to provide an improved methodand an improved aluminum and magnesium laminated body which avoids theforegoing difficulties and which also enables the use of a magnesiumcore that is readily rolled or otherwise worked.

,Other objects will appear as the description of the invention proceeds.

In conformity with the present invention a composite body of aluminumand magnesium is formed by effecting a substantially uniform bondbetween the two metals under such conditions as to substantially preventdispersion of either of these metals into the other. To this end zinc orzinc alloy is first bonded to the surface of each of the aluminum andmagnesium bodies which are to be united, and then said zinc surfaces areunited under such conditions as to assure a substantially uniform bondthroughout the united surfaces by integrating said zince layers underconditions which substantially prevent dispersion of the magnesium andaluminum into each other. Thereby are avoided the discontinuities andirregularities of bond which would exist if the metals were rolled orotherwise pressed together, while at the same time no hard or brittlealuminum-magnesium layer is established between the two metals tointerfere with satisfactory rolling and other working of the laminatedmetal.

By suitably controlling the temperatures employed the character andthicknes of bond may be closely controlled and predetermined.

For most purposes it is preferable to hav the coating metalsubstantially coextensive with the outer face of the ultimate product,but it is within the contemplation of the present invention to providean aluminum coating on one or more faces only. Furthermore, while it ispreferred to form the laminated metal in the form of a billet block orslab, it is to be expressly understood that the invention is notrestricted thereto as the composite metal may be formed, in conformitywith the present invention, in other shapes that are appropriate for theultimate products to be produced. Therefore the term "slab as usedherein is to be construed as a term generic to any suitable form of bodyin which the aluminum is united to the magnesium as hereinafterexplained.

While a magnesium core may be cast in the form of a billet or block, itis preferred that the magnesium core be subjected before laminating themetal as cast in order that the laminated metal may be more easilyrolled or otherwise worked.

The surface layer or layers may be composed of pure aluminum or anysuitable aluminum base: alloy, depending upon the character of coatindesired, and similarly the core may be composed of pure magnesium or anysuitable magnesium base alloy, depending upon the character of coredesired. Therefore it is to be expressly under stood that when aluminumor magnesium are referred to herein it is intended to embrace not onlythe pure metals but any suitable alloys thereof. Furthermore, where zincis herein referred to as used in the bonding layer it is to beunderstood, as will appear more fully hereinafter, that suitable zincalloys may also be used, and therefore when the term zinc is used hereinit is intended to embrace any suitable alloy thereof as well a the puremetal.

The preferred procedure in practicing the present invention is asfollows:

A slab of magnesium or magnesium alloy, of any suitable size anddimensions, is first formed in any suitable way, as by procedures knownto the art. Preferably the magnesium is first cast into a billet whichis then turned on a lathe or otherwise suitably worked to remove thecast skin. The said cast billet is then extruded into a slab to refinethe grain. The slab so formed may be of any suitable dimensions, saythre inches thick, nine inches wide and fifty-four inches long. If awider core is desired this slab may then be preheated to a temperaturebetween 750 and 800 F., and then cross rolled to the desired width, forexample, eighteen inches.

The rolled slab is then heated to any suitable temperature above themelting point of zinc, or the zinc alloy to be used, say a temperatureon the order of 950 F., and then a layer of zinc or zinc alloy isapplied to a face thereof, preferably by vigorously scratchbrushing thesurface of the magnesium while molten zinc is uniformly distributed overthe surface thereof, so that a strong and substantially uniform bond isestablished between the zinc and the magnesium. This layer may becomposed of pure zinc or any suitable zinc alloy such as the magnesiumzinc eutectic containing about 5% magnesium.

An aluminum facing sheet of the same size as the magnesium slab isprepared, either before or after the aforesaid preparation of the magnesium core, and this is also provided at its face which is to be unitedto the magnesium core with a similar layer of zinc or suitable zincalloy. This zinc layer may be formed on the aluminum sheet in the samemanner as that heretofore referred to for forming the zinc layer on themagnesium core, i. e., by vigorously scratchbrushing the surface of thealuminum heated to a temperature above the melting point of the zinc orzinc alloy to be used, say on the order of 950 F., while molten zinc orzinc alloy is uniformly distributed over the surface of the aluminum, toestablish a strong and substantially uniform bond there with. Here also,either pure zinc or a suitable zinc alloy such as the zinc aluminumeutectic containing approximately 5% aluminum may be the same tooperations that refine the grain of used.

The aluminum facing layer may be of any suitable thickness, as thethickness may be varied within relatively wide limits, depending uponthe use to which the composite metal is to be put, the desiredcharacteristics in the ultimate product, etc. Thus for a magnesium slabsay 1 inches thick the aluminum facing layer may be on the order of aquarter of an inch thick, but as before indicated this aluminum facinglayer may be made materially thinner or materially thicker dependingupon the characteristics and properties desired. The aluminum facinglayer is preferably formed from hot rolled sheets, as this provides afacing layer which is well annealed and has a relatively clean surface.However, cold rolled aluminum sheets may be employed if preferredprovided they are sufficiently annealed and the surface thereof properlycleaned to enable the carrying out of the herein described process.

The zinc layers applied to the magnesium and aluminum are preferably ofsuch thickness that under the treatment by which they are applied thezinc does not disperse completely into the metal to which it is beingapplied, but there is a substantial layer of relatively pure zinc orzinc alloy remaining at the face when the treatment is completed, whileeffecting a strong and substantially uniform bond between'the zinc orzinc alloy and the magnesium and aluminum respectively. To this end thepreferred procedure isto heat the magnesium or the aluminum, as the casemay be, to a temperature at least as high as and preferably somewhatabove the eutectic melting points of the aluminum-zinc or magnesium-zincbinary systems respectively. The zinc is then applied, preferably in amolten condition although if preferred the heat of the slab or sheet maybe used to melt the zinc, to that face of the magnesium or aluminum thatis to be united with the other in such a way as to assure a uniformbreak down and detachment of the oxide film on the metal to which thezinc or zinc alloy is being applied while obtaining the desired depth ofbond. To this end the metal to which the zinc or zinc alloy is beingapplied may first be treated with any suitable flux to break down theoxide, but a vigorous brushing of the molten zinc into the base metal,as by a suitable wire brush, after the molten metal, whether applied assuch or melted by the temperature of the base metal, has been spreaduniformly over the surface of the base metal, is preferred because itwill by abrasion sufficiently break down the oxide film while protectingthe surface of the base metal from contact with the air and avoiding thepresence of foreign material that may have to be removed to avoidformation of gas or other interference with the desired establishment ofa uniform bond between the laminations;

The depth of the bond formed can be varied depending upon thetemperature of the base metal, the quantity of zinc or zinc alloy usedin each layer, and the time and character of the mechanical or chemicalwork which is used in breaking -down the oxide film and assuring thepenetration of the zinc or zinc alloy into the metal to which it isapplied. Ordinarily a relatively suing description, the magnesium coreis disposed between the two aluminum facing layers with the zincsurfaces of the latter in contact with the zinc surfaces on themagnesium core, forming a sandwich of the magnesium between the aluminumlaminations. This sandwich is then heated to a suitable temperaturebelow the melting temperatures of the aluminum and magnesium and thecontacting zinc layers are then united under pressure. Variousprocedures may be followed to effect this result.

According to one procedure the sandwich may be heated to a temperatureabove the melting temperature of the zinc or zinc alloy layers, butbelow the melting temperatures of magnesium and aluminum, say to atemperature of 900 F. The sandwich is then placed in a hydraulic orother suitable press and such pressure is applied thereto as to effectan integration of the molten zinc layers so as to produce a continuousand homogeneous weld between said zinc layers. The laminated metal isthen allowed to cool below the melting temperature of the zinc,whereupon it may be rolled in the customary manner to sheets, foil,etc., of any suitable thickness. If wider sheets are desired, crossrolling may be employed. In these rolling operations the metal ispreferably rolled hot but with the temperature sufliciently below themelting point of the zinc so that the heat produced during the rollingoperation will not cause the zinc to melt and cause delamination of thealuminum and magnesium.

A second procedure that may be followed is to heat the sandwich whileheld together by steel straps, wires or the like to a temperaturesomewhat below the melting point of the zinc, say around 700 F., andthen subject the sandwich to one or more rolling operations, utilizingthe heat produced by the rolling operation to raise the temperatureabove the melting point of the zinc and thereby produce a welded bond.As soon as a secure bond has been established the straps, wires or thelike may be removed. and the rolling continued as-above referred to.

The subsequent rolling operations may be performed in accordance withpractices well understood in the art, with or without; preheating;annealing, etc., between rollings, depending on the core metal used, thesize and thickness of the laminated body, the character of the ultimateproduct desired, etc.

By suitably controlling the temperatures the depth and character of thebond between the thin alloy layer is desired, because deep penetrationof the zinc into the base metal creates a layer of alloy which is lessductile than the base metal, while a substantial coat of the zinc orzinc alloy at the surface of the slab or sheet is desired for thewelding operation hereinafter reat both faces thereof for the purpose ofthe en- '75 laminations may be nicely controlled, but as substantialpenetration of the magnesium into the aluminum or vice versa isundesirable, the temperature relationships are preferably so maintained,having regard to the character and thickness of the zinc or zinc alloylayers employed, that no appreciable dispersion of the magnesium andaluminum into each other is permitted. These same considerations shouldalso govern the temperatures at which subsequent rollings and workingsare effected, having regard also for the amount of heat generated as aresult of such operations.

Aluminum coated magnesium plates, sheets, foils, etc., of suitablethickness may thereby be formed for fabrication into a wide variety ofarticles and the composite metal so formed possesses the advantagesderived from the use of the lighter weight magnesium as a core materialwhile the magnesium is properly encased and protected by the corrosionresistant aluminum.

The accompanying drawing illustrates diagrammatically on an enlargedscale, and without regard to proper proportions for the laminae, analuminum coated magnesium sheet as produced by the present invention.While a facing layer is shown at only one side of the core, it will beunderstood that facing layers may be applied to both sides of .the core.

The present invention therefore provides slabs or other bodies ofaluminum coated magnesium wherein the magnesium and aluminum are unitedthroughout their contiguous surfaces by a substantially uniform bondwhile avoiding relatively hard and brittle aluminum-magnesium layersthat interfere with subsequent rolling and working of the compositemetal. The composite metal is possessed of the various desirablecharacteristics inherent in the use of aluminum as a coating metal andmagnesium as a core metal without detraction from their relativecharacteristics by the manner in which this composite metal is formed.The improved method of the present invention assures the establishmentof the desired bond between, the metals under conditions which mayreadily be carried out in largescale operations and the resulting.product, because of its characteristics as assured by the method ofproduction, may be put to a wide variety of uses 'in the electrical,mechanical and chemical arts where the light weight of magnesium makessuch desirable and a wide variety of objects may be made therefrom.

' While the preferred procedure has been de-- scribed with considerableparticularity, it is to be expressly understood that the invention isnot to be restricted thereto, as various departures therefrom will nowsuggest themselves to those skilled in the art. Other methods forestablishing the zinc or zinc alloy layers and uniting them into asecure and permanent bond, and other methods of treatment of theresulting composite metal, will now readily suggest themselves to thoseskilled in the art. Reference is therefore to be had to the claimshereto appended for a definition of the limits of the invention.

What is claimed is:

1. The method of forming laminated sheets, plates and other bodies ofaluminum coated magnesium which includes the steps of forming amagnesium core, substantially destroying the oxide film at the surfaceof the magnesium to be united to the aluminum by forming a. zinc layeralloyed to the face of the magnesium, forming one or more aluminumsheets, substantially destroying the oxide film at the surface of thealuminum to be united to the magnesium by forming a zinc layer alloyedto the aluminum, placing said zinc layers on the magnesium and aluminumdirectly in contact, integrating said zinc layers, and thereafterrolling the laminated slab so formed.

. 2. The method of forming laminated sheets, plates and other bodies ofaluminum coated mag nesium which includes the steps of forming amagnesium core, substantially destroying the oxide film at the surfaceof the magnesium to be united to the aluminum by forming a zinc layeralloyed to the face of the magnesium, forming one or more aluminumsheets, substantially destroying the oxide film at the surface of thealuminum to be united to the magnesium by forming a zinc layer alloyedto the aluminum, placing said zinc layers on the magnesium and aluminumdirectly in contact and fusing said zinc layers together under heat andpressure, and

3. The method of forming laminated sheets, plates and other bodies ofaluminum coated magnesium which includes the steps of forming amagnesium core, substantially destroying the oxide film at the surfaceof the magnesium to be united to the aluminum by forming a'zinc layeralloyed to the face of the magnesium, forming one or more aluminumsheets, substantially destroying the oxide film at the surface of thealuminum to be united to the magnesium by forming a zinc layer alloyedto the aluminum, placing said zinc layers on'the magnesium and aluminumdirectly in contact while the laminations are heated to a temperatureabove the melting point of the zinc layers, welding said zinc layerstogether, and thereafter rolling the laminated slab so formed.

4. The method of forming laminated slabs anti other bodies of aluminumcoated magnesium which includes the steps of casting a magnesium body,refining the grain of the magnesium by extruding the cast magnesium bodyto form a magnesium slab, forming a substantially continuouspredetermined layer of zinc on one or both faces of said slab, formingone or more aluminum sheets of substantially the size of said slab,forming a substantially continuous predetermined layer of zinc on a faceof each sheet, placing said zinc layers on the magnesium and aluminum indirect contact, and integrating said zinc layers.

5. The method of forming laminated slabs and other bodies of aluminumcoated magnesium which includes the steps of casting a magnesium body,refining the grain of the magnesium by extruding the cast magnesium bodyto form a magnesium slab, forming a substantially continuouspredetermined layer of zinc on one or both faces of said slab, formingone or more aluminum sheets of substantially the size of said slab,forming a substantially continuous predetermined layer of zinc on a faceof each sheet, placing said zinc layers on the magnesium and aluminum indirect contact, and fusing said zinc layers together under heat andpressure.

6. The method of forming laminated slabs and other bodies of aluminumcoated magnesium which includes the steps of casting a magnesium body,refining the grain of the magnesium by extruding the cast magnesium bodyto form a magnesium slab, forming a substantially continuouspredetermined layer of zinc on one or both faces of said core, formingone or more aluminum sheets of substantially the size of said slab,forming a substantially continuous predetermined layer of zinc on a faceof each sheet, placing said zinc layers on the magnesium and aluminum indirect contact while the laminations are heated to a temperature abovthe melting point of the zinc, and welding said zinc layers together.

7. The method of laminating aluminum and magnesium to form malleablealuminum coated I magnesium which includes the steps of formingthereafterrolling the laminated slab so formed. 7

a magnesium core, applying molten zinc to said magnesium core whilebreaking down the magnesium oxide film thereon to form a predeterminedzinc layer on the magnesium, forming one or more aluminum sheets ofsubstantially the same size as said magnesium core, applying molten zincto the aluminum while breaking down the aluminum oxide film thereon toform a predetermined zinc layer thereon, placing said zinc layers on themagnesium and aluminum in direct contact, and integrating said zinclayers.

8. The method of laminating aluminum and magnesium to form malleablealuminum coated magnesium which includes the steps of forming amagnesium core, applying molten zinc to said magnesium core whilebreaking down the magnesium oxidefilm thereon to form a predeterminedzinc layer on the magnesium, forming one or more aluminum sheets ofsubstantially the same size as said magnesium core, applying molten zincto the aluminum while breaking down the aluminum oxide film thereon toform a predetermined zinc layer thereon, placing said zinc layers on themagnesium and aluminum in direct contact, and fusing said zinc layerstogether under heat and pressure.

9. The method of laminating aluminum and magnesium to form malleablealuminum coated magnesium which includes the steps of forming amagnesium core, applying molten zincto said magnesium core whilebreaking down the mag-. nesium oxide film thereon to form apredetermined zinc layer on the magnesium, forming one or more aluminumsheets of substantially the same size as said magnesium core, applyingmolten zinc tothe aluminum while breaking down the aluminum oxide filmthereon to form a predetermined zinc layer thereon, placing said.

zinc layers on the magnesium and aluminum in direct contact while thelaminations are heated to a temperature above the melting point of thezinc, and welding said zinclayers together.

10. The method of coating magnesium with aluminum in forming laminatedsheets, plates and other bodies of aluminum coated magnesium whichincludes the steps of forming magnesium having alloyed to the facethereof a thin coating of zinc, forming aluminum having alloyed to theface thereof a thin coating of zinc, placing said zinc layers on themagnesium and aluminum in direct contact, and integrating said zinclayers into a malleablebond.

11. The method of coating magnesium with aluminum in forming laminatedsheets, plates and other bodies of aluminum coated magnesium whichincludes the steps of forming magnesium having alloyed to the facethereof a thin coating of zinc, forming aluminum having alloyed to theface thereof a thin coating of zinc, placing said zinc layers on themagnesium and aluminum in direct contact, and homogeneously fusing saidaluminum coating and a magnesium core united zinc layers together underheat and pressure into and other bodies of aluminum coated magnesium bya substantially continuous bond of zinc alloyed to the aluminum and themagnesium and of suficient thickness to prevent substantial dispersionof the magnesium and aluminum into each other, said zinc layer beingsubstantially coextensive with the contiguous surfaces of the magnesiumand aluminum and directly and uniformly bonded to both.

14. The method of forming laminated sheets, plates ond other bodies ofaluminum coated magnesium which includes the steps of casting amagnesium body, extruding the cast magnesium body to form a magnesiumslab, substantially destroying the oxide film at the surface of themagnesium to be united to the aluminum by forming a zinc layer alloyedto the face of the magnesium, forming one or more aluminum sheets,substantially destroying the oxide film at the surface of the aluminumto be united to the magnesium by forming a zinc layer alloyed to thealuminum, placing said Zinc layers on the magnesium. and aluminumdirectly in contact, in-

-the surface of the aluminum to be united to the magnesium by forming azinc layer alloyed to the aluminum, placing said zinc layers on themagnesium and aluminum directly in contact, heating the laminations to atemperature above the melting point of the zinc layers, fusing said zinclayers together, and thereafter rolling the laminated slab so formed.

= ERNEST SCHELLER.

